Identification of CD34+/PGDFRα+ Valve Interstitial Cells (VICs) in Human Aortic Valves: Association of Their Abundance, Morphology and Spatial Organization with Early Calcific Remodeling

Ultrastructural evidence of telocytes in the embryonic chick heart

The cardiac telocyte (TC) is a novel interstitial cell type with a unique ultrastructure and great potential in therapy. The present study examined its presence in the heart of chicken embryos ageing 7-15 days old (Hamburger-Hamilton [HH] stages 31-41) using transmission electron microscopy. TCs were identified across all stages in the atrial and ventricular myocardium, close to maturing cardiomyocytes, blood vessels and lymphatics. Early-stage TCs have immature features resembling mesenchymal cells. Late-stage TCs were distinct, possessing the cytoplasmic prolongations termed telopodes (Tps), which are very long and thin, usually 1-3 in number, and display a moniliform appearance and have an average thickness below 0.2 μm. TCs residing in the epicardium and endocardium were also detected. In the subepicardium near developing coronary vessels, they were localized in the cardiac stem cell niches, coexisting with cardiac stem cells and cardiomyocyte progenitors. Electron-dense structures and the release of extracellular vesicles were observed between embryonic TCs and surrounding structures, suggesting roles in intercellular communication, cardiomyocyte differentiation and maturation, angiogenesis, and stem cell nursing and guidance.

Telocytes response to cardiac growth induced by resistance exercise training and endurance exercise training in adult male rats

Telocytes are interstitial cells found in different tissues, including cardiac stem cell niches. The purpose of this study was to investigate the response of the telocytes to the cardiac growth that occurs in response to resistance and endurance exercise trainings using rats distributed into control, endurance, and resistance training groups. Results revealed that the ratio of heart weight to body weight, cardiomycyte number, cardiomyocyte area, thickness of the left ventricular wall were significantly higher in the training groups compared to the control group. We observed increment in the cardiomyocytes surface area and thickness of the left ventricular wall in the resistance-training group than endurance-training group. We conclude that both resistance and endurance exercise trainings will lead to an increased number of cardiac telocytes, consequently, promote activity of the cardiac stem cells, and results in physiological cardiac growth, and this response does not seem to depend on the type of exercise.

The two facets of receptor tyrosine kinase in cardiovascular calcification-can tyrosine kinase inhibitors benefit cardiovascular system?

Tyrosine kinase inhibitors (TKIs) are widely used in cancer treatment due to their effectiveness in cancer cell killing. However, an off-target of this agent limits its success. Cardiotoxicity-associated TKIs have been widely reported. Tyrosine kinase is involved in many regulatory processes in a cell, and it is involved in cancer formation. Recent evidence suggests the role of tyrosine kinase in cardiovascular calcification, specifically, the calcification of heart vessels and valves. Herein, we summarized the accumulating evidence of the crucial role of receptor tyrosine kinase (RTK) in cardiovascular calcification and provided the potential clinical implication of TKIs-related ectopic calcification. We found that RTKs, depending on the ligand and tissue, can induce or suppress cardiovascular calcification. Therefore, RTKs may have varying effects on ectopic calcification. Additionally, in the context of cardiovascular calcification, TKIs do not always relate to an unfavored outcome-they might offer benefits in some cases.

Towards Personalized Therapy of Aortic Stenosis

Calcific aortic stenosis (CAS) is the most common cause of acquired valvular heart disease in adults with no available pharmacological treatment to inhibit the disease progression to date. This review provides an up-to-date overview of current knowledge of molecular mechanisms underlying CAS pathobiology and the related treatment pathways. Particular attention is paid to current randomized trials investigating medical treatment of CAS, including strategies based on lipid-lowering and antihypertensive therapies, phosphate and calcium metabolism, and novel therapeutic targets such as valvular oxidative stress, coagulation proteins, matrix metalloproteinases, and accumulation of advanced glycation end products.

Aortic valve cell microenvironment: Considerations for developing a valve-on-chip

Cardiac valves are sophisticated, dynamic structures residing in a complex mechanical and hemodynamic environment. Cardiac valve disease is an active and progressive disease resulting in severe socioeconomic burden, especially in the elderly. Valve disease also leads to a 50% increase in the possibility of associated cardiovascular events. Yet, valve replacement remains the standard of treatment with early detection, mitigation, and alternate therapeutic strategies still lacking. Effective study models are required to further elucidate disease mechanisms and diagnostic and therapeutic strategies. Organ-on-chip models offer a unique and powerful environment that incorporates the ease and reproducibility of in vitro systems along with the complexity and physiological recapitulation of the in vivo system. The key to developing effective valve-on-chip models is maintaining the cell and tissue-level microenvironment relevant to the study application. This review outlines the various components and factors that comprise and/or affect the cell microenvironment that ought to be considered while constructing a valve-on-chip model. This review also dives into the advancements made toward constructing valve-on-chip models with a specific focus on the aortic valve, that is, in vitro studies incorporating three-dimensional co-culture models that incorporate relevant extracellular matrices and mechanical and hemodynamic cues.

Cardiac Telocytes 16 Years on-What Have We Learned So Far, and How Close Are We to Routine Application of the Knowledge in Cardiovascular Regenerative Medicine?

The regeneration of a diseased heart is one of the principal challenges of modern cardiovascular medicine. There has been ongoing research on stem-cell-based therapeutic approaches. A cell population called telocytes (TCs) described only 16 years ago largely contributed to the research area of cardiovascular regeneration. TCs are cells with small bodies and extremely long cytoplasmic projections called telopodes, described in all layers of the heart wall. Their functions include cell-to-cell signaling, stem-cell nursing, mechanical support, and immunoregulation, to name but a few. The functional derangement or quantitative loss of TCs has been implicated in the pathogenesis of myocardial infarction, heart failure, arrhythmias, and many other conditions. The exact pathomechanisms are still unknown, but the loss of regulative, integrative, and nursing functions of TCs may provide important clues. Therefore, a viable avenue in the future modern management of these conditions is TC-based cell therapy. TCs have been previously transplanted into a mouse model of myocardial infarction with promising results. Tandem transplantation with stem cells may provide additional benefit; however, many underresearched areas need to be addressed in future research before routine application of TC-based cell therapy in human subjects. These include the standardization of protocols for isolation, cultivation, and transplantation, quantitative optimization of TC transplants, cost-effectivity analysis, and many others.

Hypoxic Culture Maintains Cell Growth of the Primary Human Valve Interstitial Cells with Stemness

The characterization of aortic valve interstitial cells (VICs) cultured under optimal conditions is essential for understanding the molecular mechanisms underlying aortic valve stenosis. Here, we propose 2% hypoxia as an optimum VIC culture condition. Leaflets harvested from patients with aortic valve regurgitation were digested using collagenase and VICs were cultured under the 2% hypoxic condition. A significant increase in VIC growth was observed in 2% hypoxia (hypo-VICs), compared to normoxia (normo-VICs). RNA-sequencing revealed that downregulation of oxidative stress-marker genes (such as superoxide dismutase) and upregulation of cell cycle accelerators (such as cyclins) occurred in hypo-VICs. Accumulation of reactive oxygen species was observed in normo-VICs, indicating that low oxygen tension can avoid oxidative stress with cell-cycle arrest. Further mRNA quantifications revealed significant upregulation of several mesenchymal and hematopoietic progenitor markers, including CD34, in hypo-VICs. The stemness of hypo-VICs was confirmed using osteoblast differentiation assays, indicating that hypoxic culture is beneficial for maintaining growth and stemness, as well as for avoiding senescence via oxidative stress. The availability of hypoxic culture was also demonstrated in the molecular screening using proteomics. Therefore, hypoxic culture can be helpful for the identification of therapeutic targets and the evaluation of VIC molecular functions in vitro.

Telocytes promote hepatocellular carcinoma by activating the ERK signaling pathway and miR-942-3p/MMP9 axis

In China, hepatocellular carcinoma (HCC) is considered a malignant tumor with poor prognosis, frequent metastasis, and a high relapse rate. Telocytes (TCs) participate in tumorigenic, invasive, and migratory processes by secreting functional proteins and transmitting cell-to-cell information, but their functions in HCC are still unknown. TC counts and MMP9 expression in liver cancer tissues were measured using immunohistochemistry, western blotting, and RT-PCR. Primary TCs from liver para-cancer tissues were cultured in vitro. To verify the role of TCs in HCC, a metastatic cancer animal model was established using three types of liver cancer cell lines in vivo. TCs promoted HCC cell metastasis by MMP9 expression in vitro and in vivo. Platelet-derived growth factor-alpha (PDGF-α), secreted by HCC cells, activated the Ras/ERK signaling pathway in TCs, thereby increasing MMP9 expression; Moreover, miR-942-3p suppressed MMP9 expression in TCs. Our results reveal the role of TCs in HCC and the mechanisms by which they elicit their effects, and they may serve as novel prognostic markers for HCC.

Morphological Evidence of Telocytes in Skeletal Muscle Interstitium of Exercised and Sedentary Rodents

Skeletal muscle atrophy, resulting from states of hypokinesis or immobilization, leads to morphological, metabolic, and functional changes within the muscle tissue, a large variety of which are supported by the stromal cells populating the interstitium. Telocytes represent a recently discovered population of stromal cells, which has been increasingly identified in several human organs and appears to participate in sustaining cross-talk, promoting regenerative mechanisms and supporting differentiation of local stem cell niche. The aim of this morphologic study was to investigate the presence of Telocytes in the tibialis anterior muscle of healthy rats undergoing an endurance training protocol for either 4 weeks or 16 weeks compared to sedentary rats. Histomorphometric analysis of muscle fibers diameter revealed muscle atrophy in sedentary rats. Telocytes were identified by double-positive immunofluorescence staining for CD34/CD117 and CD34/vimentin. The results showed that Telocytes were significantly reduced in sedentary rats at 16 weeks, while rats subjected to regular exercise maintained a stable Telocytes population after 16 weeks. Understanding of the relationship between Telocytes and exercise offers new chances in the field of regenerative medicine, suggesting possible triggers for Telocytes in sarcopenia and other musculoskeletal disorders, promoting adapted physical activity and rehabilitation programmes in clinical practice.

Cd34+ Stromal Cells/Telocytes in Normal and Pathological Skin

We studied CD34+ stromal cells/telocytes (CD34+SCs/TCs) in pathologic skin, after briefly examining them in normal conditions. We confirm previous studies by other authors in the normal dermis regarding CD34+SC/TC characteristics and distribution around vessels, nerves and cutaneous annexes, highlighting their practical absence in the papillary dermis and presence in the bulge region of perifollicular groups of very small CD34+ stromal cells. In non-tumoral skin pathology, we studied examples of the principal histologic patterns in which CD34+SCs/TCs have (1) a fundamental pathophysiological role, including (a) fibrosing/sclerosing diseases, such as systemic sclerosis, with loss of CD34+SCs/TCs and presence of stromal cells co-expressing CD34 and αSMA, and (b) metabolic degenerative processes, including basophilic degeneration of collagen, with stromal cells/telocytes in close association with degenerative fibrils, and cutaneous myxoid cysts with spindle-shaped, stellate and bulky vacuolated CD34+ stromal cells, and (2) a secondary reactive role, encompassing dermatitis—e.g., interface (erythema multiforme), acantholytic (pemphigus, Hailey–Hailey disease), lichenoid (lichen planus), subepidermal vesicular (bullous pemphigoid), psoriasiform (psoriasis), granulomatous (granuloma annulare)—vasculitis (leukocytoclastic and lymphocytic vasculitis), folliculitis, perifolliculitis and inflammation of the sweat and sebaceous glands (perifolliculitis and rosacea) and infectious dermatitis (verruca vulgaris). In skin tumor and tumor-like conditions, we studied examples of those in which CD34+ stromal cells are (1) the neoplastic component (dermatofibrosarcoma protuberans, sclerotic fibroma and solitary fibrous tumor), (2) a neoplastic component with varying presentation (fibroepithelial polyp and superficial myxofibrosarcoma) and (3) a reactive component in other tumor/tumor-like cell lines, such as those deriving from vessel periendothelial cells (myopericytoma), epithelial cells (trichoepithelioma, nevus sebaceous of Jadassohn and seborrheic keratosis), Merkel cells (Merkel cell carcinoma), melanocytes (dermal melanocytic nevi) and Schwann cells (neurofibroma and granular cell tumor).

Telocytes and Other Interstitial Cells: From Structure to Function

The Special Issue, "Telocytes and Other Interstitial Cells: From Structure to Function" of the International Journal of Molecular Sciences, is dedicated to recent progress in research on interstitial cells [...].